Photosynthetic capacity varies hugely within an individual over time, between individuals in different environments, and between species. Demming-Adams et al. review the processes that affect intrinsic photosynthetic capacity. Plants modulate their intrinsic photosynthetic capacity according to input (e.g., shade-grown plants generally have a lower capacity than plants growing in bright light), and demand (e.g., rate of export of photosynthetic products from the leaf and sink strength). Photosynthetic capacity can be governed by light harvesting capacity or CO2-fixing capacity and is affected by transport capacity, leaf thickness, developmental stage, temperature, stress and other factors. Understanding these factors can lead to increases in crop productivity. Curr. Opin. Plant Biol. 10.1016/j.pbi.2017.03.008